Method and system for performing regenerative braking with feedback from brake-traction control system

ABSTRACT

Methods and systems for operating a vehicle on a reduced traction surface are disclosed. A controller of the vehicle obtains at least one of: ambient information or GPS information, determines a derate increment size based on the ambient or GPS information, imposes a sustained derate by applying a torque limit on a braking torque of the vehicle based on the derate increment size in response to detecting a traction control event. The controller also determines a verification period and a derate reduction period based on the ambient or GPS information to reduce the sustained derate in response to detecting a lack of traction control event during the verification period at a rate determined by the derate reduction period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/085,845, filed Oct. 30, 2020, the disclosure of which is incorporatedby reference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to hybrid vehicles, especiallyto improving braking and traction control of the hybrid vehicles.

BACKGROUND OF THE DISCLOSURE

Environmental concerns and limited natural resources are highlightingthe desire for reduced fuel consumption. One promising avenue toward thereduction of fuel consumption is the use of hybrid and electricpowertrains. Such powertrains utilize regenerative braking to increasethe overall efficiency of the system. Regenerative braking providesnegative torque to the driveline and recovers kinetic energy from amoving vehicle, which is stored as electrical potential energy. Vehiclesmay also include other types of braking systems that create negativetorque, such as compression release braking and exhaust braking, and ofcourse accelerator pedals to create positive torque.

Most vehicles today are provided with a traction control system, such asan anti-lock brake system (ABS). The traction control system detectsloss of traction between the wheels and the road surface such as mayoccur during a torque change. The traction control system intervenes inresponse to a traction control event during a torque change by sending acommand to the engine/motor controller or retarder controller to deratetraction and/or retard torque on the driveline during the tractioncontrol event. When the traction control event is over, the derate isremoved at a controlled rate to avoid problems with a suddenreapplication of torque. There is no lasting effect of one of thesetemporary derates, beyond the duration of the event itself.

In presently available hybrid and electric powertrain systems,regenerative and other braking is typically triggered by means otherthan actuation of the brake pedal, such as at the low end of theaccelerator pedal when it is lifted or released. As a result, by liftingof the accelerator pedal a significant amount of braking isautomatically applied, which may create a traction control event inslick conditions. Since the amount of negative torque that is applied ispredetermined and typically based on dry road conditions and otherfactors, and with a significant amount of regenerate braking beingautomatically applied whenever the driver releases the acceleratorpedal, poor traction road conditions are likely to produce multipletraction control events. This is because the same amount of retardertorque is re-applied to the powertrain each time the accelerator pedalis released, regardless of any history of traction loss. It would bedesirable for the braking control system to mitigate the likelihood offuture traction loss by taking action to reduce regenerative brakinglimits automatically. Simply offering a dashboard switch to turn off orreduce regenerative braking could result in energy capture beingdisabled long-term, even with favorable road conditions. Therefore,further technological developments are desirable in this area.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure relate to methods andsystems to detect a loss of traction via digital information conveyed byan onboard ABS device. A method of operating a vehicle on a reducedtraction surface includes the controller of the vehicle obtaining atleast one of ambient information or GPS information, determining aderate increment size based on the ambient information or the GPSinformation, and, in response to detecting a traction control event,imposing a sustained derate by applying a torque limit on a brakingtorque of the vehicle based on the derate increment size.

In some examples, the method includes the controller incrementallyincreasing the sustained derate on the braking torque based on thederate increment size in response to detecting subsequent tractioncontrol event. In some examples, the method includes the controllerdetermining a verification period based on the ambient information orthe GPS information and in response to detecting a lack of tractioncontrol event during the verification period, determining to remove thetorque limit.

In some examples, the method includes the controller determining aderate reduction period based on the ambient information or the GPSinformation and reducing the sustained derate at a rate determined bythe derate reduction period in response to determining to removing thetorque limit. In some examples, the derate increment size, theverification period, and the derate reduction period are greater whenthe ambient information or the GPS information indicates a loweratmospheric temperature. In some examples, the lower atmospherictemperature is at or below 0° C.

In some examples, the ambient information used in the method includesone or more of: atmospheric temperature, atmospheric pressure, weathercondition, humidity, or precipitation. In some examples, detecting thetraction control event includes interpreting a signal from a tractioncontrol system of the vehicle indicative of a loss of traction. In someexamples, the traction control system is an anti-lock brake system ofthe vehicle.

In some examples, imposing the sustained derate further includes one of:derating a negative braking torque or derating a positive drive torque.In some examples, imposing the sustained derate further includeslimiting the negative braking torque applied by regenerative braking. Insome examples, imposing the sustained derate further includes limitingthe negative braking torque applied by compression release braking. Insome examples, imposing the sustained derate further includes limitingthe negative braking torque applied by exhaust braking.

Further disclosed herein are apparatuses for operating a vehicle on areduced traction surface. The apparatus includes a controller whichobtains at least one of ambient information or GPS information,determines a derate increment size based on the ambient information orthe GPS information, and imposes a sustained derate by applying a torquelimit on a braking torque of the vehicle based on the derate incrementsize in response to detecting a traction control event.

In some examples, the controller also incrementally increases thesustained derate on the braking torque based on the derate incrementsize in response to detecting subsequent traction control event. In someexamples, the controller further determines a verification period basedon the ambient information or the GPS information and determines toremove the torque limit in response to detecting a lack of tractioncontrol event during the verification period.

In some examples, the controller also determines a derate reductionperiod based on the ambient information or the GPS information andreduces the sustained derate based on the derate reduction period inresponse to detecting a lack of traction control event during the deratereduction period. In some examples, the derate increment size, theverification period, and the derate reduction period are greater whenthe ambient information or the GPS information indicates a loweratmospheric temperature. In some examples, the lower atmospherictemperature is at or below 0° C.

In some examples, the ambient information used by the apparatus includesone or more of: atmospheric temperature, atmospheric pressure, weathercondition, humidity, or precipitation. In some examples, the controllerdetects the traction control event by interpreting a signal from atraction control system of the vehicle indicative of a loss of traction.In some examples, the controller imposes the sustained derate byderating a negative braking torque or derating a positive drive torque.

Also disclosed herein are vehicle systems including a drive unit with aprime mover and a controller coupled with the drive unit. The controllercan obtain at least one of: ambient information or GPS information,determine a derate increment size, a verification period, and a deratereduction period based on the ambient information or the GPSinformation, impose a sustained derate to the drive unit in response todetecting a traction control event by applying a torque limit on abraking torque of the drive unit based on the derate increment size,determine to remove the torque limit in response to detecting a lack oftraction control event during the verification period, and reduce thesustained derate based on the derate reduction period in response todetecting a lack of traction control event during the derate reductionperiod.

While multiple embodiments are disclosed, still other embodiments of thepresent disclosure will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the disclosure. Accordingly, the drawingsand detailed description are to be regarded as illustrative in natureand not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be more readily understood in view of the followingdescription when accompanied by the below figures and wherein likereference numerals represent like elements. These depicted embodimentsare to be understood as illustrative of the disclosure and not aslimiting in any way.

FIGS. 1A and 1B are schematic block diagrams of a vehicle with atraction control system according to embodiments disclosed herein;

FIG. 2 is a schematic block diagram of a controller that functionallyexecutes certain operations for managing traction control events as wellas devices and systems to be used in conjunction with the controller,according to embodiments disclosed herein;

FIGS. 3A and 3B are graphs showing drive cycle torque limit on reducedtraction surface as known in the art;

FIGS. 4A through 4D are graphs showing drive cycle torque limit onreduced traction surface according to embodiments disclosed herein;

FIGS. 5A through 5D are graphs showing drive cycle torque limit onreduced traction surface according to embodiments disclosed herein;

FIGS. 6A through 6D are graphs showing drive cycle torque limit onreduced traction surface according to embodiments disclosed herein;

FIG. 7 is a schematic flow diagram of a procedure for managing tractioncontrol events according to embodiments disclosed herein; and

FIG. 8 is a schematic flow diagram of another procedure for managingtraction control events according to embodiments disclosed herein.

While the present disclosure is amenable to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and are described in detail below. Theintention, however, is not to limit the present disclosure to theparticular embodiments described. On the contrary, the presentdisclosure is intended to cover all modifications, equivalents, andalternatives falling within the scope of the present disclosure asdefined by the appended claims.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the present disclosureis practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present disclosure, andit is to be understood that other embodiments can be utilized and thatstructural changes can be made without departing from the scope of thepresent disclosure. Therefore, the following detailed description is notto be taken in a limiting sense, and the scope of the present disclosureis defined by the appended claims and their equivalents.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment. Similarly, the use of theterm “implementation” means an implementation having a particularfeature, structure, or characteristic described in connection with oneor more embodiments of the present disclosure, however, absent anexpress correlation to indicate otherwise, an implementation may beassociated with one or more embodiments. Furthermore, the describedfeatures, structures, or characteristics of the subject matter describedherein may be combined in any suitable manner in one or moreembodiments.

Referencing FIG. 1A, a vehicle system 100 includes a vehicle 101. Thesystem 100 further includes a powertrain or a drive unit 114 having aprime mover 103. The prime mover 103 may include an internal combustionengine and/or one or more electric devices selectively coupled to adrive shaft 105. The prime mover 103 may be any type of internalcombustion engine and/or electric motor known in the art arranged toprovide a hybrid powertrain, an electric powertrain, or an internalcombustion engine powertrain. In the example of FIG. 1A, the prime mover103 is coupled to the driveshaft 105 through a transmission 107. Adifferential 115 couples the driveshaft 105 with the wheels 108.

The system 100 further includes an optional electrical energy storagedevice 116 that can be connected to prime mover 103. Electrical energystorage device 116 is electrically connected to store electricitygenerated by the vehicle 101. The electrical energy storage device 116can be a battery such as a lithium ion battery, a lead-acid battery, anickel metal hydride battery, or any other device capable of storingelectrical energy. In certain embodiments, energy may be storednon-electrically, for example in a high performance fly wheel, in acompressed air tank, and/or through deflection of a high capacityspring. Where the energy is stored electrically, any electrical energystorage device 116 is contemplated herein, including a hyper-capacitorand/or an ultra-capacitor.

In certain embodiments, the system 100 includes the drive shaft 105mechanically coupling the prime mover 103 to two or more vehicle drivewheels 108A and 108B. The system 100 may include any other type of loadother than or in addition to drive wheels 108, for example any load thatincludes stored kinetic energy that may intermittently be slowed by anybraking device included in the power train or drive unit 114. Anexemplary system 100 includes one or more mechanical braking devicesresponsive to a mechanical braking command.

An exemplary mechanical braking device includes a compression brakingdevice (not shown), for example a device that adjusts the valve timingof a prime mover that includes an engine such that the engine becomes atorque absorber rather than a torque producer. Another exemplarymechanical braking device includes an exhaust throttle (or exhaustbrake) that, in moving toward a closed position, partially blocks anexhaust stream and applies back pressure on the engine resulting in anegative crankshaft torque amount. Yet another exemplary mechanicalbraking device is a variable geometry turbocharger (VGT) device that canbe adjusted to produce back pressure on the engine and provide a brakingeffect. Still another exemplary mechanical braking device includes ahydraulic retarder. The hydraulic retarder is typically incorporatedwith the transmission 107. The mechanical braking device may be anybraking device which is not the conventional friction brakes of thevehicle 12, and the described examples are not exclusive.

The system 100 further includes a torque request device 109 thatprovides a torque request value. An exemplary deceleration requestdevice comprises a throttle pedal position sensor. However, any deviceunderstood in the art to provide a torque request value, or a value thatcan be correlated to a present negative torque change request orpositive torque change request for the powertrain or drive unit 114 iscontemplated herein. As used herein, negative braking torque includesvehicle braking provided by or able to be provided by the powertrain 14without friction braking.

System 100 also includes a traction control system 111 connected to oneor more wheels 108. Traction control system 111 is configured to detecta traction control event associated with wheels 108. In certainembodiments, the traction control event is a loss of traction determinedby, for example, an antilock brake system (ABS) 113 and indicative of areduced traction surface. For example, the loss of traction can bedetected by ABS 113 in response to one or more of wheels 108 slipping ona road surface. A traction control event signal is provided tocontroller 102 to derate the nominal torque applied by powertrain ordrive unit 114 to wheels 108 to reduce slippage in response to thetraction control event. Hereinafter, a traction control event is alsoreferred to as an “ABS event” because the existence of such event causesthe ABS 113 to respond.

As discussed further below, controller 102 is configured toincrementally change the derate torque applied by powertrain or driveunit 114 over a number of traction control events to gradually reducethe nominal torque. After a predetermined period of time expires with notraction control events, the incrementally reduced derate torque isreleased to gradually return to the nominal derate torque. In oneembodiment, this allows fuel economy to be increased by more fullyutilizing available regenerative braking torque capacity during tractioncontrol events. The incremental changes to the derate torque and thegradual return of the derate torque to the nominal derate torque arecontrolled by the controller 102 based on the measured ambienttemperature and/or GPS information, for example, as explained below.

The controller 102 of system 100 may include modules structured tofunctionally execute operations for managing the torque derate ofpowertrain or drive unit 114. The controller 102 is linked to the torquerequest device 111 and the powertrain or drive unit 114. In certainembodiments, the controller 102 forms a portion of a processingsubsystem including one or more computing devices having memory,processing, and communication hardware. The controller 102 may be asingle device or a distributed device, and the functions of thecontroller 102 may be performed by hardware or instructions encoded on acomputer readable medium.

As shown in FIG. 1B, another example of a vehicle system 100A. Thesystem 100A includes a controller 102, a brake master cylinder 104controlled by the controller 102, a brake 110 with a brake-pressuremodulation valve 106 controlling it, and a motor and drive unit 114coupled to wheels 108. For simplicity, only two wheels 108A and 108B(e.g., front wheel or rear wheels) of a vehicle is shown, but it isunderstood that the ABS may include components configured to performanti-lock capability on additional sets of wheels, as suitable. Eachwheel 108 has a corresponding sensor 112A or 112B to take measurementsincluding but not limited to speed of the vehicle. An energy storagedevice 116 is coupled with the motor in the motor and drive unit 114. Itis to be understood that, although not shown, other components such asengine and transmission may be included if the vehicle is a hybridvehicle, and an inverter may also be included in the system to convertthe DC power to AC power to drive the motor, for example.

Each solid connection in FIG. 1B represents a mechanical coupling suchas via mechanical parts or pipes, whereas each broken line represents anelectrical coupling such as via wired or wireless connections. When thebrakes 110 (e.g., brakes 110A and 110B coupled with the wheels 108A and108B, respectively) are applied, fluid is forced from the brake mastercylinder 104 through the pipes, where pressure is transmitted throughsolenoid valves or brake-pressure modulation valves 106, which are partsof a hydraulic control unit (HCU). The sensors 112 detect the operationof the wheels 108, and when the controller 102 detects conditions in thewheels 108 (as measured by the sensors 112) indicating that the wheels108 are about to lock, the controller 102 closes the valves 106 (forexample, valves 106A and 106B as coupled with brakes 110A and 110B) andprevents any more fluid from entering the circuit. The locking of thevalves 106 remain until the controller 102 detects that the wheels 108are no longer decelerating, as measured by the sensors 112.

The electric motor implemented in the motor and drive unit 114 can beused in braking as well in the form of regenerative braking. When thebrake pedal is pressed, the motor is treated as a generator to producenegative torque, in which case the produced energy is dissipated or usedto chare the energy storage device 116, such as batteries.

FIG. 2 illustrates the subcomponents of the controller 102 according tosome examples. The controller 102 has an ABS derate module 200 and areceiver/transmitter 206 set. The ABS derate module 200 includes aprocessing unit 202 and a memory storage device 204. The processing unit202 may be any suitable processor, e.g. a central processing unit (CPU),a system on a chip (SoC), or a multi-chip module (MCM), etc., asapplicable, and the memory storage device 204 may be any suitable deviceto hold data regarding programs, instructions, algorithms, and othertypes of information, to be accessed and executed by the processing unit202. The memory storage device 204 may be a random-access memory (RAM),read-only memory (ROM), flash memory, or any other types of suitabledata storage devices.

The receiver/transmitter 206 is capable of receiving and transmittingdata in the form of signals via wired and/or wireless communications. Insome examples, the receiver/transmitter 206 allows the controller 102 toaccess a plurality of external components outside of the vehicle, suchas ambient thermometer 208 to measure the ambient air temperaturesurrounding the vehicle, GPS 210 to detect location of the vehicle, anduser interface 212 to receive input from the user, who may be theoperator or driver of the vehicle. The controller 102 in some examplesis also capable of receiving data from a weather information system 214which may be an application software on a mobile device, or websiteaccessible via the Internet. Alternatively, the weather informationsystem 214 may include a radio channel that reports the weatherinformation. The weather information may be provided visually,auditorily, or via encrypted data. The controller 102 may include amodule which transcribes the visual or auditory information into a formof data that is usable by the ABS derate module 200 for furtherprocessing. In some examples, the wired connection may include a serialcable, a fiber optic cable, a CAT5 cable, or any other form of wiredconnection. The wireless connections may include the Internet, Wi-Fi,cellular, radio, Bluetooth, ZigBee, etc. In some examples, a controllerarea network (CAN) bus provides the exchange of signals, information,and/or data. The CAN bus includes any number of wired and wirelessconnections.

While the term “processor” is briefly defined above, the terms“processor” and “processing unit” are meant to be broadly interpreted.In this regard and as mentioned above, the “processor” may beimplemented as one or more general-purpose processors, applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), digital signal processors (DSPs), or other suitable electronicdata processing components structured to execute instructions providedby memory. The one or more processors may take the form of a single coreprocessor, multi-core processor (e.g., a dual core processor, triplecore processor, quad core processor, etc.), microprocessor, etc. In someembodiments, the one or more processors may be external to theapparatus, for example, the one or more processors may be a remoteprocessor (e.g., a cloud based processor). Alternatively oradditionally, the one or more processors may be internal and/or local tothe apparatus. In this regard, a given circuit or components thereof maybe disposed locally (e.g., as part of a local server, a local computingsystem, etc.) or remotely (e.g., as part of a remote server such as acloud based server).

In some examples, the controller 102 operates such that, upon occurrenceof a momentary braking torque derate event triggered by the onboard ABSdevice (e.g., the sensors 112 detecting measurements indicative of suchevent), the controller 102 establishes a permanent incremental deratesuch that when the ABS derate event ends, the maximum allowed brakingtorque is diminished from what was allowed before the traction controlevent, or the ABS event. The permanent derate may be stored in thememory storage 204 and updated as more occurrences of the momentarybraking torque derate event are detected by the controller 102. Uponeach subsequent ABS derate event, the controller 102 incrementallytightens the permanent braking torque derate, permitting less and lessallowed braking torque with each ABS event. Alternatively, when there isan extended period with no ABS derate events, the controller 102 mayslowly release the permanent derate, eventually allowing full brakingtorque again.

Momentary braking torque derate events are known to occur morefrequently on slick roads than on dry pavements. FIGS. 3A and 3Billustrate a baseline case of a drive cycle on reduced traction surface,with ABS events implemented according to a previously known ABS controlmethod during a time window of 500 seconds. In FIG. 3A, the vehicle istraveling along a surface with variable torque measurements within thedrive cycle. Regenerative braking torque regularly enters or “dips” intoa torque range that could cause traction problems on slick roadconditions. On dry roads, there are no traction problems and no ABSevents, so there would be no total torque limit that is implemented, butwhen the road is a reduced traction surface, this torque range causesthe vehicle to experience numerous ABS derate events (marked by thesmall spikes in the lower line of the graph, indicated as “ABS event”).

Large braking torques cause traction losses and trigger ABS derateevents. In response, the ABS reacts by dramatically increasing a totaltorque limit 300 (marked by the large spikes in the upper line of thegraph in FIG. 3B) during these ABS events. These are merely “spikes”because, as soon as the ABS event ends, the increase in the total torquelimit also ends, allowing the vehicle to travel in the same manner asbefore the ABS event. As shown in these graphs, the ABS repeats thisprocess each time an ABS event is detected, thereby making each one a“momentary” braking torque derate event. As such, during a tractioncontrol event, the ABS commands a momentary derate to regain tractionand then relinquishes control such that full braking torque range isonce again available. No sustained torque limiting is enforced afterimmediate symptoms of the traction event are corrected.

The methods described herein reduce the likelihood of repeated tractioncontrol events on slick surfaces and require no change to existingconventional ABS devices and resides entirely within the regenerativebraking controller. The techniques described in this disclosure couldalso be applied to other braking methods, such as engine compressionbraking or exhaust braking.

FIGS. 4A through 4D illustrate an example of incremental derating andincremental releasing of the derating for a drive cycle on reducedtraction surface, according to embodiments disclosed herein. A totaltorque limit 400 (broken line) is shown to increase incrementally from 0to approximately 200 seconds with each ABS event, after which there is asustained verification period 402 where the controller observes if anyadditional ABS event takes place. If no ABS event occurs, no change ismade to the total torque limit 400, i.e. no further derating orreduction in the derating. In some examples, a timer is used to measurethe length of time after the previous ABS event, such that when adetermined length of time (i.e. the verification period 402) passeswithout any ABS event, the torque limit is allowed to be reduced.

After the verification period 402 ends with no further ABS event, thetorque limit is gradually reduced or “ramped down” to the formerno-derate value, as shown in a derate reduction period 404. Thereduction or ramping down of the torque limit 400 depends on numerousfactors as further explained herein. The length of the ramp, or the rateat which the reduction takes place, also varies based on these factors,as determined by the controller. In this example, a verification periodof 20 minutes with no ABS events permits gradual relaxation of derateover a derate reduction period of 25 minutes.

The methods disclosed are applicable to braking methods other thanregenerative braking and therefore does not require an electric drive.Electric and hybrid drive vehicles, particularly with the lowaccelerator pedal braking, offer benefit in applying the methodsdisclosed herein because of the frequent and unavoidable brakingapplication. Those of ordinary skills in the art would understand thatthe basic technique of these methods may be applied to compressionbraking torque limits as well. Alternatively, the methods disclosedherein are not limited to the braking torque applications, but may beapplied such that positive traction torque may be derated in the same orsimilar manner, as suitable. In some examples, it may also be desirableto take no permanent action following the first one or two tractionevents, in order to prevent the controller from causing derates due to asmall patch of loose gravel or sand on the road surface, for example.The methods may be applied to mitigate traction control problems inslick road conditions over a wider area, such as may be experienced inwinter or rainy conditions, for example.

FIGS. 5A through 5D illustrate an example of incremental derating andincremental releasing of the derating for a drive cycle on reducedtraction surface at a lower atmospheric temperature, according toembodiments disclosed herein. A total torque limit 500 (broken line) isshown to be imposed on the system at approximately 60 seconds, which iswhen the first and only ABS event is detected. Based on the factors asdescribed herein, the controller determines to set the torque limit 500at a predetermined derate level in a single, large increment that islarger than any single increment shown in the torque limit 400.Afterwards, there is a sustained verification period 502 where no changeis made to the total torque limit 500, i.e. no further derating orreduction in the derating, as long as the ABS events stop occurring. Thetorque limit 500 is then allowed to relax the derate in a deratereduction period 504. In this example, the verification period of 30minutes with no ABS events permits gradual relaxation of derate over aderate reduction period of 25 minutes.

The difference in the torque limits 400 and 500 results from thedifferent ambient or environmental conditions. The torque limit 400occurs in a relatively warm environment, where the ambient temperatureis above a freezing point of water (0° C.), for example. When theambient temperature is colder, such as close to, at, or below water'sfreezing point, the reduced traction surface is not only wet from thewater located on the surface, but the water may be partially or entirelyfrozen to cause ice to cover at least a part of the surface, therebyfurther reducing the traction. In some cold driving conditions, even asingle ABS event can cause vehicle yaw (side-to-side motion) that adriver may consider dangerous. In these cases, it may be desirable tohave a driver-activated regenerative braking derate to prevent even thesingle slip event (ABS event). However, simply offering a dashboardswitch to turn off or reduce regenerative braking may result in energycapture being disabled on a long-term basis, even with favorable roadconditions.

Therefore, in the present method, upon the first detection of an ABSevent at approximately 60 seconds, the controller in FIGS. 5A through 5Dsets the torque limit 500 at a predetermined torque limit level with asingle, large increment. Because of the cold temperature, theverification period 502 for the torque limit 500 is longer than theverification period 402 for the torque limit 400, which adds anadditional layer of safety for the driver. Furthermore, although thederate reduction period 504 is shown as being the same the deratereduction period 404, in some examples, the derate reduction period 504can be longer than the derate reduction period 404 when the temperatureis colder, in response to the controller determining that a suddenderate may likely be performed based on factors such as weather and roadconditions, for example.

In some examples, a driver-activated dashboard switch is used inconjunction with the present method by treating the switch activation asan ABS event. That is, on switch activation, the controller reduces thebraking limit as though an ABS event had occurred. The reduction may bethe same increment as would occur for a single, actual ABS event, or thereduction could be the maximum allowed reduction. Alternatively, thereduction may be an amount that varies with the ambient temperature.After switch activation, the controller measures a duration of time withneither another switch activation nor an ABS event. When the durationlasts longer than the determined verification period, the derate isrelaxed back to a no-derate condition at a rate determined by the deratereduction period. Subsequent switch activations repeats this sameeffect. Through this means, a dashboard switch could be utilized thatwould not unnecessarily impair energy capture for an extended period oftime. Such driver-activated dashboard switch may be implemented as partof the user interface 212 as shown in FIG. 2 .

FIGS. 6A through 6D illustrate an example of incremental derating andincremental releasing of the derating for a drive cycle on reducedtraction surface at a higher atmospheric temperature, according toembodiments disclosed herein. A total torque limit 600 (broken line) isshown to be imposed on the system until approximately 190 seconds. Thereare numerous ADS events occurring during this time, and at each event,the torque limit 600 increases incrementally as shown. Afterwards, thereis a sustained verification period 602 where no change is made to thetotal torque limit 600, i.e. no further derating or reduction in thederating, as long as the ABS events stop occurring. The torque limit 600is then allowed to relax the derate in a derate reduction period 604. Inthis example, the verification period of 5 minutes with no ABS eventspermits gradual relaxation of derate over a derate reduction period of 3to 4 minutes.

The verification period 602 and the derate reduction period 604 of thetorque limit 600 are both shorter than those determined in previousexamples (torque limits 400 and 500) because the atmospheric temperatureis higher than in the previous examples. In a warm ambient environment,the controller imposes a moderate, sustained derate on braking torquethat increments up on each ABS event, until the ABS events quitoccurring. In such environment, water on the road surface does notfreeze into ice, and in some examples, when the weather condition issunny and dry, the water may even evaporate or be absorbed into theearth, thereby increasing traction on the road surface. In this regard,the atmospheric and environmental information obtained may include theweather condition, which may include humidity and/or precipitation (or,alternatively, lack thereof), for example, in addition to temperature.

Referring further to FIG. 7 , an algorithm, process, method, orprocedure 700 as performed or implemented by a controller. The procedure700 includes step 702 to obtain ambient information and/or GPSinformation. In step 704, the controller detects a traction controlevent. Procedure 700 continues at conditional step 706 to determine witha previous traction control event occurred in a predetermined timethreshold. If conditional step 706 is positive, procedure 700 continuesat step 708 to incrementally derate the torque that is applied to thepowertrain or drive unit in response to the traction control event.Procedure 700 continues from step 708 at step 704 to detect a subsequenttraction control event. In some examples, the procedure 700 continuesfrom step 708 to step 702 to update the ambient and/or GPS information,as suitable.

If conditional step 706 is negative, procedure 700 continues atconditional step 710 to determine if a torque derate increment from thenominal or maximum derate torque is active. If conditional step 710 isnegative procedure 700 returns to step 702 or 704. If conditional step710 is positive, procedure 700 continues at step 712 to incrementallyrelease the torque derate from the incremented torque derate toward themaximum or nominal torque derate so that the torque derate graduallyreturns toward the maximum or nominal torque derate. Procedure 700returns from step 712 to step 702 or 704, as suitable.

Procedure 700 includes detecting a plurality of traction control eventsfor a vehicle in which the vehicle loses traction with a road surface ateach traction control event. Procedure 700 further includes, in responseto detecting each of the plurality of traction control events,incrementally derating a torque applied to a powertrain of the vehiclefor each subsequent traction control event relative to a previoustraction control event. In certain embodiments of procedure 700,detecting the traction control event includes interpreting a signal froma traction control system of the vehicle indicative of a loss oftraction. In further embodiments, the traction control system is ananti-lock brake system of the vehicle.

In other embodiments of procedure 700, derating the torque furtherincludes one of derating a negative braking torque and derating apositive drive torque. Derating the torque may further include limitingor reducing incrementally the negative braking torque applied byregenerative braking. Derating the torque may also include limiting orreducing incrementally the negative braking torque applied bycompression release braking. Derating the torque may also includelimiting or reducing incrementally the negative braking torque appliedby exhaust braking.

In other embodiments, procedure 700 includes incrementally derating thetorque for a plurality of traction control events detected over apredetermined period of time, where the increment of the derating isbased on the ambient and/or GPS information. After an expiration of aperiod of time since a last traction control event, procedure 700includes incrementally releasing or increasing the derating of torquetoward a maximum allowable torque to be applied to the powertrain inresponse to the traction control event, where the increment of thereleasing or increasing of the derating is based on the ambient and/orGPS information. In other embodiment, procedure 700 includesincrementally derating the torque only after two or more tractioncontrol events are detected, where the increment of the derating isbased on the ambient and/or GPS information.

Referring further to FIG. 8 , an algorithm, process, method, orprocedure 800 as performed or implemented by a controller. The procedure800 includes step 802 to obtain ambient information and/or GPSinformation. The procedure 800 also includes step 804 to determine (a)an increment size, (b) a verification period, and (c) a derate reductionperiod based on the obtained ambient and/or GPS information. Thereafter,at conditional step 806, the controller determines if a traction controlevent is detected. If no such event is detected, in step 810, thevehicle is allowed to operate without derating, after which theprocedure 800 returns to step 802. If a traction control event isdetected in step 806, the procedure 800 proceeds to step 808 to impose asustained derate on the braking torque using the determined incrementsize from step 804. The increment size may be smaller for a warmeratmospheric temperature and larger for a colder atmospheric temperature,for example.

The controller then detects subsequent traction control event, if any,in step 812. For each detected traction control event, in step 814, thederate is incrementally increased on each traction control event usingthe increment size determined in step 804. The steps 812 and 814 arerepeated until there is no detected traction control event. Inconditional step 816, the controller determines if the verificationperiod (determined in step 804) has passed without any traction controlevent. If any traction control event takes place during this period, thetimer is reset and the procedure 800 returns to step 812. Otherwise, ifno traction control event occurs during the verification period, thetorque limit is gradually decreased in step 818 based on the deratereduction period determined in step 804. The derate reduction period maybe longer for a colder atmospheric temperature and shorter for a warmeratmospheric temperature, for example.

The procedure 800 may be repeated from step 802 or step 806, assuitable. If new ambient information is detected or the new GPSinformation indicates that the vehicle has traveled to a new region thathas different atmospheric conditions from before, the controller maydecide to update the ambient information and/or GPS information todetermine new values for the verification period, increment size, andderate reduction period.

As previously mentioned, the environmental conditions include but arenot limited to atmospheric temperature and weather/environmentalconditions. Different environmental conditions may dictate vastlydifferent choices for both derate magnitude and duration. Asillustrative examples, a transit bus in Aspen in January may encountericy, snowy, or slippery roads that persist for hours, and for whichmultiple slip events could have severe consequences. On the other hand,a transit bus in Tucson in August may encounter an extremely wet road,possibly resulting in large puddles, or some sand or gravel debris thatis highly localized. As such, these encounters are unlikely to last morethan a minute and do not pose as severe a danger as slipping on glareice. Utilizing the same reaction to both scenarios either underperformsin Aspen or overreacts in Tucson.

Therefore, the presently disclosure describes different operatingscenarios that may be driven by seasonal weather conditions (or othervariables, as further disclosed herein). In winter conditions, thetraction control events are more severe because of both the likelihoodof slippage and the resulting extreme friction reduction due to ice orsnow on the surface. In comparison, summer or warmer weather conditionsare unlikely to have as severe a reduction in road friction as ice orsnow, nor are likely to exist over as wide a geographical area.Utilizing an ambient air temperature sensor, for example, will give thecontroller critical information to help differentiate these differentconditions. In cold ambient temperatures, the magnitude of thepost-ABS-event (or post-traction control event) derate increment can beincreased, and the sustained duration of this derate can be extended. Inwarm ambient temperatures, the magnitude of the derate increment can besmaller such that a vehicle could tolerate multiple ABS events ifnecessary to produce a severe derate, and the derate can be phased outsooner. Additionally, in some examples, altitude may also affect theverification period, increment size, and a derate reduction periodbecause the freezing point of water increase as altitude increases andthe atmospheric pressure decreases correspondingly. Although the changein freezing point may be slight, the inclusion of such environmentalinformation in some examples increases the accuracy of the procedures asimplemented.

As is evident from the figures and text presented above, a variety ofembodiments according to the present invention are contemplated. In someexamples, detecting the traction control event includes interpreting asignal from a traction control system of the vehicle indicative of aloss of traction. In some examples, the traction control system is ananti-lock brake system of the vehicle. In some examples, derating thetorque further includes one of derating a negative braking torque andderating a positive drive torque. In some examples, derating the torquefurther includes limiting the negative braking torque applied byregenerative braking. In further examples, derating the torque furtherincludes limiting the negative braking torque applied by compressionrelease braking. In yet other examples, derating the torque furtherincludes limiting the negative braking torque applied by exhaustbraking.

In some examples, the controller is configured to incrementally derate anegative braking torque applied by a regenerative braking system. Insome examples, the controller is configured to incrementally derate anegative braking torque applied by at least one of a compression releasebraking system and an exhaust brake. In yet other examples, thecontroller is configured to incrementally derate a positive torqueapplied by at least one of a motor and an internal combustion engine ofthe drivetrain.

In some examples, a system is provided that includes a powertrain and acontroller. The powertrain includes at least one of an internalcombustion engine and an electrical device, and the powertrain isconnected to a plurality of wheels and a traction control system. Thecontroller is in communication with the traction control system and atleast one of the engine and the electrical device. The controller isconfigured to receive a traction control event signal from the tractioncontrol system indicating a loss of traction of the wheels, and thecontroller is further configured to incrementally derate a torqueapplied to the powertrain relative to a torque derate for a previoustraction control event in response to the traction control event signal.

In one embodiment, the electrical device is operably coupled to anelectrical energy storage device. In another embodiment, the torquederate is a negative torque. In a further embodiment, the torque derateis a positive torque.

The present subject matter may be embodied in other specific formswithout departing from the scope of the present disclosure. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. Those skilled in the art willrecognize that other implementations consistent with the disclosedembodiments are possible. The above detailed description and theexamples described therein have been presented for the purposes ofillustration and description only and not for limitation. For example,the operations described can be done in any suitable manner. The methodscan be performed in any suitable order while still providing thedescribed operation and results. It is therefore contemplated that thepresent embodiments cover any and all modifications, variations, orequivalents that fall within the scope of the basic underlyingprinciples disclosed above and claimed herein. Furthermore, while theabove description describes hardware in the form of a processorexecuting code, hardware in the form of a state machine, or dedicatedlogic capable of producing the same effect, other structures are alsocontemplated.

What is claimed is:
 1. A method of operating a vehicle on a reducedtraction surface, the method comprising: detecting, by a controller ofthe vehicle, that the vehicle is operating under a sustained derate inwhich a torque limit is applied on a maximum allowed braking torque ofthe vehicle; obtaining, by the controller, at least one of: ambientinformation or GPS information; determining, by the controller, anincrement size by which the torque limit is configured to be changed,the increment size being based on the ambient information or the GPSinformation; and in response to detecting a lack of traction controlevent indicative of a loss of traction by the vehicle, incrementallyremoving, by the controller, the torque limit on the maximum allowedbraking torque based on the increment size.
 2. The method of claim 1,further comprising: determining, by the controller, a verificationperiod based on the ambient information or the GPS information; and inresponse to detecting the lack of traction control event during theverification period, incrementally removing, by the controller, thetorque limit on the maximum allowed braking torque based on theincrement size.
 3. The method of claim 2, further comprising:determining, by the controller, a derate reduction period based on theambient information or the GPS information; and in response to detectingthe lack of traction control event during the verification period,incrementally removing, by the controller, the torque limit on themaximum allowed braking torque at a rate determined by the deratereduction period.
 4. The method of claim 3, further comprising:increasing, by the controller, the increment size, the verificationperiod, or the derate reduction period in response to detecting, basedon the ambient information or the GPS information, a reduction in anatmospheric temperature.
 5. The method of claim 3, further comprising:increasing, by the controller, the increment size, the verificationperiod, or the derate reduction period in response to detecting, basedon the ambient information or the GPS information, that an atmospherictemperature is at or below 0° C.
 6. The method of claim 1, wherein theambient information includes one or more of: atmospheric temperature,atmospheric pressure, weather condition, humidity, or precipitation. 7.The method of claim 1, wherein the sustained derate is indicative of alimit being applied on a negative braking torque or on a positive drivetorque of the vehicle.
 8. An apparatus for operating a vehicle on areduced traction surface comprising: a controller configured to: detectthat the vehicle is operating under a sustained derate in which a torquelimit is applied on a maximum allowed braking torque of the vehicle;obtain at least one of: ambient information or GPS information;determine an increment size by which the torque limit is configured tobe changed, the increment size being based on the ambient information orthe GPS information; and in response to detecting a lack of tractioncontrol event indicative of a loss of traction by the vehicle,incrementally remove the torque limit on the maximum allowed brakingtorque based on the increment size.
 9. The apparatus of claim 8, whereinthe controller is further configured to: determine a verification periodbased on the ambient information or the GPS information; and in responseto detecting the lack of traction control event during the verificationperiod, incrementally remove the torque limit on the maximum allowedbraking torque based on the increment size.
 10. The apparatus of claim9, wherein the controller is further configured to: determine a deratereduction period based on the ambient information or the GPSinformation; and in response to detecting the lack of traction controlevent during the verification period, incrementally remove the torquelimit on the maximum allowed braking torque at a rate determined by thederate reduction period.
 11. The apparatus of claim 10, wherein thecontroller is further configured to: increase the increment size, theverification period, or the derate reduction period in response todetecting, based on the ambient information or the GPS information, areduction in an atmospheric temperature.
 12. The apparatus of claim 10,wherein the controller is further configured to: increase the incrementsize, the verification period, or the derate reduction period inresponse to detecting, based on the ambient information or the GPSinformation, that an atmospheric temperature is at or below 0° C. 13.The apparatus of claim 8, wherein the ambient information includes oneor more of: atmospheric temperature, atmospheric pressure, weathercondition, humidity, or precipitation.
 14. The apparatus of claim 8,wherein the sustained derate is indicative of a limit being applied on anegative braking torque or on a positive drive torque of the vehicle.15. A vehicle system comprising: a drive unit including a prime mover;and a controller coupled with the drive unit, the controller configuredto: detect that the vehicle is operating under a sustained derate inwhich a torque limit is applied on a maximum allowed braking torque ofthe vehicle; obtain at least one of: ambient information or GPSinformation; determine an increment size by which the torque limit isconfigured to be changed, the increment size being based on the ambientinformation or the GPS information; and in response to detecting a lackof traction control event indicative of a loss of traction by thevehicle, incrementally remove the torque limit on the maximum allowedbraking torque based on the increment size.